Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $210.32   11.577%   $234.6687   $234.67   $234.65   $234.70  
  Purchase #2 $217.99   12.323%   $244.8529   $244.85   $244.85   $244.90  
  Purchase #3 $38.98   4.455%   $40.7166   $40.72   $40.70   $40.70  
  Purchase #4 $99.27   5.542%   $104.7715   $104.77   $104.75   $104.80  
  Purchase #5 $128.92   10.166%   $142.026   $142.03   $142.05   $142.00  
  Purchase #6 $10.48   13.185%   $11.8618   $11.86   $11.85   $11.90  
  Purchase #7 $160.88   10.858%   $178.3484   $178.35   $178.35   $178.30  
  7 purchase totals = $866.84       $957.2459   $957.25   $957.20   $957.30